DEM-Digital Elevation Model; Hillshade

http://developmentseed.org/blog/2009/jul/30/using-open-source-tools-make-elevation-maps-afghanistan-and-pakistan/

Depicted above is a Digital Elevation Model of some mountains and the surrounding country. DEM's are useful in showing vertical data in several ways. Above is a hillshade, a rendering of elevation data to show shadows and depressions, and a color relief map to more easily contrast land features like mountains. Numerical data is often difficult to understand, and before computer technology it was only more so. With satellite imagery and hillshade models it has become infinitely more easy to represent elevation data in a visual manner.

http://developmentseed.org/blog/2009/jul/30/using-open-source-tools-make-elevation-maps-afghanistan-and-pakistan/

Here are the two separate images of the elevation rendering(top) and the color relief map(bottom), combined to create a hillshade